Yes, the problems that befell Chelsea last season did affect the team, so their performance decreased slightly. Although many say "it shouldn't lower their performance" But we don't know for sure what happened to the team as a whole. Because what we know is what appears on the outside. It's very difficult for Chelsea to stay optimal in these circumstances.
What is certain is that Chelsea will continue to try to improve their performance at the beginning of next season even though what appears from the outside is a decline in performance because it is triggered by problems that existed last season. But overall Chelsea are still trying to make his team's performance improve next season.
How can chelsea improve its performance if there was not good player interested to join in the club? the current chelsea's player have no capacity to compete with another club. The new skillful players are actually needed by the club but sadly they were rejecting chelsea's offer. Arsenal has been going so hard in the transfer season unlike chelsea which has been denied so many times by good players. This is a disaster for this club.
Will chelsea become mediocre soon? who knows.